Introduction

• Metamorphic rocks are formed from pre-existing rocks through heat, pressure, and chemically active fluids.
• Classification is based on texture and mineral composition.
• Two main categories: Foliated and Non-foliated rocks.
• Note: Metamorphic rocks generally do not have specific names; they are usually descriptive.

Foliated Metamorphic Rocks

1. Slate
2. Phyllite
3. Schist
4. Gneiss

• Foliation: Planar arrangement of mineral grains, giving the rock a layered or banded appearance.

Slate

• Texture: Very fine-grained, slaty cleavage.
• Common minerals: Quartz, mica, chlorite.
• Description: Derived from shale; low-grade metamorphism.

Source: https://openpress.usask.ca

Phyllite

• Texture: Fine-grained, wavy surfaces with a sheen.
• Common minerals: Mica, quartz, chlorite.
• Description: Higher grade than slate; has a silky sheen due to fine mica flakes.

Source: https://openpress.usask.ca

Schist

• Texture: Medium to coarse-grained, schistosity (visible foliation).
• Common minerals: Mica, quartz, feldspar, garnet.
• Description: Higher grade than phyllite; often has large mica grains.

Source: https://openpress.usask.ca

Gneiss

• Texture: Coarse-grained, banding of light and dark minerals (gneissic texture).
• Common minerals: Quartz, feldspar, biotite, amphibole.
• Description: High-grade metamorphic rock; distinct mineral banding.

Source: https://openpress.usask.ca

Non-foliated Metamorphic Rocks

• Non-foliated texture: No preferred orientation of mineral grains.

Marble

• Texture: Coarse-grained, granular.
• Common minerals: Calcite or dolomite.
• Description: Derived from limestone; reacts with acid.

Source: https://openpress.usask.ca

Quartzite

• Texture: Medium to coarse-grained, interlocking quartz grains.
• Common minerals: Quartz.
• Description: Derived from sandstone; very hard and resistant to weathering.

Source: https://openpress.usask.ca

Hornfels

• Texture: Fine-grained, dense, and hard.
• Common minerals: Variable, often with biotite, feldspar, and pyroxene.
• Description: Formed by contact metamorphism; lacks foliation.

Source: https://openpress.usask.ca

Metamorphic Rock Names

• Descriptive Naming: Metamorphic rocks do not have fixed names.
• Rock names generally describe the texture and mineral composition.
• Example: Biotite schist, Staurolite-Garnet-Mica Schist … etc